Re: [PATCH RFT 0/2/2] mtd: hyperbus: add Renesas RPC-IF driver

[Vignesh Raghavendra <vigneshr@xxxxxx>]

Hi,

On 18/02/20 12:42 pm, Behme Dirk (CM/ESO2) wrote:
> Hi Vignesh,
> 
> On 18.02.2020 05:00, Vignesh Raghavendra wrote:
>> Hi Sergei
>>
[...]
>>
>> Looking around, there seems to be more than one SPI controllers, apart
>> from Renesas, which also support SPI NOR and HyperFlash protocol within
>> a single IP block. E.g.: Cadence xSPI controller [1]. Therefore, we need
>> a generic framework to support these kind of controllers.
>>
>> One way would be to extend spi_mem_op to support above template along
>> with a new field to distinguish SPI NOR vs HyperFlash protocol. HyperBus
>> core can then register a spi_device and use spi-mem ops to talk to
>> controller driver.
>> So, I suggest making Renesas RPC-IF backend a full fledged spi-mem
>> driver (instead of driver/memory) and use extended spi_mem_op to support
>> HyperFlash.
> 
> 
> From Renesas Hyperflash user point of view, I wonder if a two step
> approach would be possible and acceptable, here?
> 
> Being a user of the Renesas Hyperflash, I want a driver for that. And,
> of course, I want it "now" ;)
> 
> So I wonder if it would be a valid option to have a functioning Renesas
> Hypeflash driver, first. And in a second step abstract that in a more
> generic way to support additional controllers. While in parallel having
> a functional driver for the Renesas people, already.
> 

AFAICS, the backend driver is not merged and is still in RFC phase.
Therefore I don't see any benefit of two step approach here. Besides
you'll have to throw away this new driver (hyperbus/rpc-if.c) entirely
later on.

How difficult is it to rewrite backend to be spi-mem driver? There is
already has a spi_mem_ops frontend implementation, so I don't see much
of an issue.
Extending hyperbus core to use spi-mem should also straight forward
Would involve moving this patch into core file.

> Is the support for [1] a more or less theoretical one, at the moment? Or
> are there users of that which need support "now", too?
> 

Its not theoretical, I do see patches for xSPI controller here:
https://patchwork.kernel.org/cover/11354193/

So, its best to sort this out now so as to avoid possible backward
compatibility issues (especially with DT bindings)

Regards
Vignesh



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